Corneal procedures can be performed that reshape the anterior surface of the cornea, and therefore change the refraction of the cornea. While the initial procedure can cause an immediate change to the shape of the anterior surface of the cornea, the cornea, after some period of time following the procedure, may respond biologically to the procedure. The biological response can modify the shape relative to the immediate post-procedure shape. The final shape of the anterior surface of the cornea therefore depends on both the change induced by the procedure as well as the biological response of the cornea. When determining how to achieve a particular refraction correction for a patient, it is therefore not only important to understand the immediate effect the procedure will have on the anterior surface of the cornea, but also any biological response the cornea may have to the procedure.
One method of changing the curvature of the anterior surface of the lens is by implanting a corneal inlay within the cornea. Some inlays do not have intrinsic power because the index of refraction of the inlay material is the same, or substantially the same, as the cornea. Thus, there is no significant refraction of light at the inlay/cornea interface. For these inlays, the entire refractive effect on the eye is achieved due to the shape change to the anterior surface of the cornea. Reshaping the anterior corneal surface is very effective in altering the optical properties of the human eye because the index of refraction difference is large at the air/anterior corneal surface boundary, i.e., the difference is 1.376−1. Very strong “bending” of light occurs at the anterior corneal surface. However, the biological response of the cornea to the inlay must also be taken into account.
For some types of inlays it was originally thought that the profile of the change to the cornea was the same as the inlay profile. For example, it was thought that the anterior surface of the inlay would translate almost or substantially exactly and cause the cornea anterior surface to assume the same shape. For corneal inlays described in U.S. patent applications: 60/776,548, filed Feb. 24, 2006; Ser. No. 11/554,544, filed Oct. 30, 2006; 61/042,659, filed Apr. 4, 2008; 61/155,433, filed Feb. 25, 2009; Ser. No. 11/738,349, filed Apr. 20, 2007; and Ser. No. 12/418,325, filed Apr. 3, 2009, which are incorporated by reference herein, however, it has empirically been shown by the Applicants that the final anterior corneal shape is not, in fact, the same as the shape of the corneal inlay. For example, the cornea's biological response to an inlay's implantation was clinically observed in U.S. Pat. No. 8,057,541, filed Oct. 30, 2006 (the disclosure of which is incorporated herein by reference), where it was observed that the central anterior surface elevation change was less than the center thickness of the inlay. The cornea's biological response to the inlays was also discussed in U.S. Pub. No. 2008/0262610, filed Apr. 20, 2007, and in U.S. Pub. No. 2009/0198325, filed Apr. 3, 2009, the disclosures of which are incorporated by reference herein. Because the final shape of the anterior surface of the cornea will not simply be the same as the shape of the inlay, the question remains how to achieve the final anterior corneal surface shape.